NEUTRON-SCATTERING STUDY OF THE INCOMMENSURATE MAGNETIC ORDER OF UNI2AL3 IN HIGH MAGNETIC-FIELDS

Elastic neutron scattering studies from a single crystal sample of the heavy fermion superconductor, UNi2Al3, have revealed the onset of lon g range magnetic order below T-N = 4.6 K. This order is characterized by an incommensurate (IC) ordering wavevector given by (1/2+/-tau, 0, 1/2) with tau=0.110+/-0.003. Measurements performed in the presence of a magnetic held (up to 8 T) perpendicular to the (H, 0, L) plane show no variation in T-N but have an effect on the intensity as well as on the IC wavevector component of the ordering wavevector. Our results a re discussed in terms of the possible basal-plane orientations for the magnetic moment in this compound.